The Plasticity of Functional Traits in the Dipterocarps of Borneo

Plasticity plays an important role in the adaptation of sessile organisms like plants to the environment. Plants have been shown to respond plastically in heterogeneous environments, with plants originating from more resource-diverse environments thought to display greater plasticity. There is also evidence that fast-growing species show greater plasticity, as acquisition of resources from resource flushes is greatly aided by faster adaptations. We tested these theories in a Bornean tropical rain forest among three soil specialization groups (clay specialists, sandy loam specialists, and generalists) using two treatments of soil (clay versus sandy loam) and two treatments of light (high versus low). Here, I address four research questions: (1) Do tree species with different soil specializations exhibit differences in the plasticity of functional traits and growth rates? (2) Does the magnitude of plasticity depend on the type of resource? (3) Do functional traits and growth rates vary in the magnitude of plasticity exhibited? (4) Is plasticity in functional traits correlated with plasticity in growth rates? Overall the results show that clay specialists and generalists are more plastic than their sandy loam counterparts. Second, on average plasticity due to light was greater than plasticity due to soil. Third, growth rates were generally more plastic than functional traits. And finally, the plasticity of functional traits and growth rates were positively correlated. These finding add important insights to the plastic response of long-lived tree species to the environment, where much remains to be explored. iii Dedication To my family, friends, and adviser who never stopped believing in me, even when I stopped believing in myself. iv Acknowledgment Many individuals contributed to this thesis, for which I shall always be grateful. I must first thank my adviser, Sabrina Russo, who gave me the opportunity to obtain a graduate education at one of the best universities in the world; and near limitless patience with me as I struggled to complete my studies. I wish to also thank my committee members Diana Pilson and John DeLong, who gave a helping hand in experimental design and data analysis when it was asked. My further gratitude to my fellow graduate students, Benjamin Reed, who all contributed ideas, questions, and input with earnestness. My thanks to Lambir Hills National Park Warden Januarie Kulis and the amiable staff from Sarawak Forestry, whose help was instrumental in conducting this research. Further gratitude to the numerous field and lab assistants who helped out with …